In the binary NiFe alloys, when the Fe content is increased to achieve a greater 4.pi.Ms, the magnetostriction increases greatly, a greater .lambda.s is also presumed to be a major contributor to read back instabilities. This prior art problem has somewhat limited the use of the binary, high Ms, NiFe alloys to write heads only. It has been reported that various compositions of the CoNiFe alloys exist where 4.pi.Ms exceeds numerical value of the conventional approximately 81/19 NiFe alloy and have near zero magnetostriction, but these films were prepared using a vacuum deposition process.
U.S. Pat. No. 4,279,707 relates to a nickel-iron electroplating composition bath which provides a permalloy utilized in current thin film heads, and operating parameters that provide excellent compositional uniformity over small topography such as the P2 or second permalloy layer in the thin film head. The techniques taught in U.S. Pat. No. 4,279,707 have been applied to prepare plated NiFe of a 45/55 alloy; however, the high values of the positive magnetostriction resulted in that the thin film heads did write well, but that the heads would not provide for the desired optimized reading due to the high positive magnetostriction.
Cobalt-nickel-iron alloys, including electroplating baths have been known in prior art patents, but the prior art has failed to recognize, most importantly, that a high cobalt content was required to obtain desired attributes for writing, as well as reading for thin film heads. The prior art compositions generally had a low level of cobalt, such as ten percent, which is contrary to the teachings of the present invention as later disclosed. Such prior art compositions are representative of U.S. Pat. Nos. 3,297,418; 3,533,922; 4,036,709; 4,242,710; and 4,430,171. The U.S. Pat. No. 3,297,418 discloses a plating bath composition for depositing NiFeCo thin films. The bath composition includes an aqueous solution of Ni, Fe and Co compounds and also H.sub.3 BO.sub.3, saccharin, and sodium lauryl sulfate. The U.S. Pat. No. 4,424,710 discloses a plating bath composition for achieving a homogeneous NiFeCo thin film deposition characterized by negative magnetostriction. The plating bath composition includes an aqueous solution of Ni, Fe and Co compounds, also H.sub.3 BO.sub.3 NaCl, Na Saccharin, and wetting agent. None of these prior art references really appreciate the utilization of a high amount of cobalt for producing a high cobalt alloy magnetic thin film, but were more concerned with nickel concentration. The references were more concerned with low cobalt concentrations with respect to the other concentrations of compositions.
U.S. Pat. No. 3,350,180 discloses a laminated magnetic film device where the magnetic material could be selected from the group including the Fe-Ni-Co alloy; although the cobalt concentration was relatively low with respect to the other compositions. The patent discloses a plating bath compositon for depositing NiFeCo thin films where the bath includes an aqueous solution of Ni, Fe and Co compounds and also H.sub.3 BO.sub.3, saccharin, and sodium lauryl sulfate.
The concern of the prior art references is that the references teach away from utilizing an electroplating bath composition for producing a high cobalt alloy magnetic thin film. The references all teach the use of a bath that plates a Ni-Fe-Co material utilizing a low percentage of cobalt material contrary to the present invention, which discloses a high percentage of cobalt material with respect to the other compositions.
The publication under Communications, of the Journal of Applied Physics, Vol. 38, pages 3409-3410, (1967), discusses "Non-magnetostrictive compositions of Fe-Ni-Co films", by C. H. Tolman, which plots the nonmagnetostrictive composition line of the Fe-Ni-Co system as illustrated in FIG. 1. The reference illustrates historically the prior art region of percentage of cobalt and the present invention region of intrinsic induction as a function of the prior art regions, as well as the present invention region.
The present invention overcomes the disadvantages of the prior art by providing an electroplating bath composition for producing a high cobalt magnetic thin film having high saturation magnetization, a magnetostriction coefficient that is substantially zero and low coercivity for use in thin film heads.